The present invention is directed toward a display device for an electronic instrument such as an electronic timepiece, and in particular to a liquid crystal display or transmission-type electrochromic display device which is of multi-layer construction. The present invention comprises a novel method of interconnection of electrodes in such a device in conjunction with means for driving particular ones of the electrodes such that activation of the corresponding display elements is either enabled or disenabled. The invention enables a higher density of display elements to be provided in such a display device, by reducing the number of external connections to the device required to apply drive signals to the electrodes thereof, for a given degree of display effectiveness in terms of such factors as overall display contrast.
At the present time, electro-optical display devices such as liquid crystal display cells are widely utilized in various types of electronic instruments, electronic calculators, timepieces, etc. Such display devices provide the advantages of only a low level of drive voltage being required and of having low power consumption, while providing a long working life with high reliability. There is at present an increasing demand for an increased density of display elements in such devices, in order to provide more complex display patterns in greater variety, in accordance with the increasing complexity of modern electronic instruments. One method of increasing the display density of a display device such as a liquid crystal cell is to utilize a time-sharing method of driving the device electrodes, to thereby reduce the number of electrical connections which must be made to the device. This is because of the fact that the limit on display element density is in general determined by the number of connections which must be made to the cell electrodes, i.e. the connections which must be made between the display device and the source of drive voltages for the display (generally an integrated circuit). Another method of increasing the maximum display element density is to utilize a multi-layer structure, i.e. to vertically stack two or more display cells such that activated display elements of the lower cell are visible through the upper cell. Such a method, however, does not in itself reduce the number of cell electrode external connections which are required. As is described hereinafter, increasing the level of time-sharing of the drive signals applied to the cell electrodes results in a decrease in display effectiveness. This is because the level of cell contrast is lowered, and the effective viewing angle of the display is reduced. Hitherto, attempts to increase the density of display elements of display cells such as liquid crystal display cells have been limited by the factors mentioned above.
With the present invention, these disadvantages of prior art display devices are substantially reduced. This is achieved by making it possible for electrodes of particular groups of display segments, which are not required to be activated simultaneously, to be connected in common. This will be made more clear by the description of preferred embodiments given hereinafter. The present invention therefore enables liquid crystal cells having a multi-layer structure to be produced, whereby a significant increase in the maximum display element density is achieved.